1. Field of the Invention
The present invention relates to a monitoring circuit monitoring actuators of an airplane, a controller controlling the operation of the actuators, and an actuator unit.
2. Description of Related Art
Control surfaces and landing gears of airplanes are conventionally operated by using actuators. The operation of actuators may be controlled by electronic control (see Japanese Unexamined Patent Publication No. 240612/2006 (Tokukai 2006-240612; Patent Document 1)).
These actuators may break down. For example, hydraulic actuators may involve fluid leakage from an output portion of the actuator (more specifically, from a piston in a cylinder), and substantially 80 percent of hydraulic actuator break down results from fluid leakage. Such fluid leakage occurs on account of deterioration or breakage of a sealing member in the actuator. In this regard, ground crew visually check the airplane for fluid leakage, either before and after the flight or at predetermined intervals. The actuator is deemed to be broken if the degree of fluid leakage exceeds a predetermined degree. After this judgment, the actuator is repaired or replaced. Such repairing and replacement or preparations for repairing and replacement take time, and hence a delay in the judgment of break down directly lowers on-time performance which is important in airplane operations.
Patent Document 2 (Japanese Unexamined Patent Publication No. 129600/1991 (Tokukaihei 3-129600)) discloses a monitoring apparatus which monitors whether an airplane which is flying is in the normal state. Monitored by this monitoring apparatus are the states of the engines, the state of the gear box, vibration of the airframe, and the like. When a value concerning each state exceeds a predetermined threshold, how long and to what extent the threshold is exceeded are recorded.
Patent Document 3 (the specification of U.S. Patent Publication No. 2008/0040152) recites a technology of monitoring the states of actuators of a flying airplane to collect information. Patent Document 3, however, fails to recite how the states of actuators are specifically monitored.